The test for diffusing capacity of the lungs (DLCO) can detect early stages of interstitial lung disease in the presence of normal spirometry and chest x-rays. This test has not been available as a screening tool because equipment to perform the DLCO test is large, expensive and generally confined to hospitals. The expense of sending patients to the hospital is high.Portable, less- expensive and easy-to-operate DLCO equipment would make this test available as a screening tool outside the hospital. Such equipment would be valuable in industry, private and group medical practices, clinics and in hospitals as a bedside test. In a Phase I grant project, the applicant has proven the feasibility of using small, diffusion-type carbon monoxide sensors in its unique diffusion module. This small module combined with a pneumotach and gas delivery system, results in a portable "diffusion spirometer" which can determine spirometry, DLCO and static lung volumes. The applicant's experience and proprietary diffusion module uniquely qualifies him to continue the development of the final design and engineering of a finished, commercial, portable "diffusion spirometer".